1. Field of the Invention
The invention relates to a flexible pouch with a mixing apparatus, the mixer shaft of which is adjustable in length, in particular for use as a bioreactor for culturing microorganisms and cells or as a mixing apparatus for media or for dissolving or suspending substances in fluids, such as for instance for producing buffer solutions.
2. Description of the Related Art
Bioreactors in which the culture medium is accommodated in flexible pouches of polymer material are obtainable over a range of volumes extending from a few liters to several hundred liters. In the case in particular of large-volume pouches, there are problems with thorough mixing of the culture medium, which is intended to ensure a uniform oxygen partial pressure. Thorough mixing is very often carried out using rotating stirring rods which consist of a mixer shaft and one or more stirring elements, such as for example propellers, and which are introduced into the interior of the pouch. Stirring elements also exist in the form of paddles or vertically vibrating mixer plates. Since with a single-use bioreactor all the parts which come into contact with cells during culturing may ideally be discarded, it is advantageous to make the mixer shaft of favorable plastics material too.
When it comes to the storage and transport of single-use bioreactors with a volume of 200 to 1000 liters, the mixer shaft, unlike the pouch, which may be folded and compressed, constitutes a problem, since its length easily exceeds the size of common packaging and storage units.
After culturing, it may also be advantageous to reduce the size of the pouch again, for example if the cell-containing culture medium is to be cooled and stored. In this case the gas located in the headspace of the pouch could be expelled, whereby the height of the pouch could as a rule be reduced by a third, which would however require a length-adjustable mixer shaft. A similar problem arises if the cells or microorganisms contained in the pouch are to be killed by heat after an abortive attempt at culturing, and the mixer shaft proves too bulky for the autoclave.
It is known from German patent application 10 2006 021 984 A1 to assemble a mixer shaft from a plurality of separate parts, with the objective of being able to equip bioreactors of different sizes with standard mixer components. It would in principle also be possible, in order to reduce the storage and transport height of the pouch, to deliver the mixer shaft in a plurality of individual parts, as described in DE 10 2006 021 984 A1, and only to assemble the mixing apparatus before it is brought into operation. However, this approach is thwarted by the fact that on delivery the separate mixer shaft parts are already presterilized inside the sterile pouch and therefore could not really be assembled into the mixer shaft without opening the sterile interior of the pouch.
The object of the invention is therefore to propose a flexible pouch with a mixing apparatus, the mixer shaft of which may be simply converted from a short transport/storage length into an extended operating length in the sterile interior of the pouch, without the sterile envelope of the bioreactor having to be opened in the process, or which may be reduced back down to its original transport/storage length without the pouch having to be opened in the process.